NAME¶
Perl::Critic::Policy::ControlStructures::ProhibitPostfixControls - Write
"if($condition){ do_something() }" instead of "do_something()
if $condition".
AFFILIATION¶
This Policy is part of the core Perl::Critic distribution.
DESCRIPTION¶
Conway discourages using postfix control structures ("if",
"for", "unless", "until", "when",
"while") because they hide control flow. The "unless" and
"until" controls are particularly evil because they lead to
double-negatives that are hard to comprehend. The only tolerable usage of a
postfix "if"/"when" is when it follows a loop break such
as "last", "next", "redo", or
"continue".
do_something() if $condition; # not ok
if ($condition) { do_something() } # ok
do_something() while $condition; # not ok
while ($condition) { do_something() } # ok
do_something() unless $condition; # not ok
do_something() unless ! $condition; # really bad
if (! $condition) { do_something() } # ok
do_something() until $condition; # not ok
do_something() until ! $condition; # really bad
while (! $condition) { do_something() } # ok
do_something($_) for @list; # not ok
LOOP:
for my $n (0..100) {
next if $condition; # ok
last LOOP if $other_condition; # also ok
next when m< 0 \z >xms; # fine too
}
CONFIGURATION¶
A set of constructs to be ignored by this policy can specified by giving a value
for 'allow' of a string of space-delimited keywords: "if",
"for", "unless", "until", "when",
and/or "while". An example of specifying allowed flow-control
structures in a
.perlcriticrc file:
[ControlStructures::ProhibitPostfixControls]
allow = for if until
By default, all postfix control keywords are prohibited.
The set of flow-control functions that are exempt from the restriction can also
be configured with the 'flowcontrol' directive in your
.perlcriticrc
file:
[ControlStructures::ProhibitPostfixControls]
flowcontrol = warn die carp croak cluck confess goto exit
This is useful if you're using additional modules that add things like
"assert" or "throw".
NOTES¶
The "die", "croak", and "confess" functions are
frequently used as flow-controls just like "next" or
"last". So this Policy does permit you to use a postfix
"if" when the statement begins with one of those functions. It is
also pretty common to use "warn", "carp", and
"cluck" with a postfix "if", so those are allowed too.
The "when" keyword was added to the language after Perl Best Practices
was written. This policy treats "when" the same way it does
"if", i.e. it's allowed after flow-control constructs. Thanks to
brian d foy for the inspiration
<
http://www.effectiveperlprogramming.com/blog/543>.
BUGS¶
Look for the "do {} while" case and change the explanation to point to
page 123 when it is found. RT #37905.
AUTHOR¶
Jeffrey Ryan Thalhammer <jeff@imaginative-software.com>
COPYRIGHT¶
Copyright (c) 2005-2011 Imaginative Software Systems. All rights reserved.
This program is free software; you can redistribute it and/or modify it under
the same terms as Perl itself. The full text of this license can be found in
the LICENSE file included with this module.